PC Gamer reports that whenever Counter-Strike: Global Offensive goes on sale, cheaters take the opportunity to re-buy the game on new Steam accounts. Hackers do this so they can cheat on the new accounts, while keeping their "real" accounts—the ones that have their libraries and items—safe and sound, should they ever get caught. The new accounts are called "smurf" accounts. Some of these are used as accounts for hacking. Some of them are just accounts that people use to circumvent matchmaking, as PC Gamer explains:

You look for a CS:GO profile with very few achievements unlocked or custom weapon skins equipped, tied to a Steam account with CS:GO as its only owned game ("Wow, such dedication. So hardcore," I usually type mockingly when I encounter one of these players). Having one or more smurfs in your match is more subtle disruption but often just as bothersome as hacking: smurf accounts don't receive a rank in the matchmaking system until they've won 10 games, allowing them to be matched with players that aren't at their true skill level.

It's a method of circumventing the matchmaking system (often as a way to play with friends who aren't near the same rank), one not unfamiliar to League of Legends players and other free-to-play games. When I'm up against such a player, there's no tool within the reporting system for me to flag their account—and why should there be? As far as Valve's concerned, that player is another legitimate customer.

Obviously that's not on the same level as using a program that lets you instantly get headshots or something, but still, it's an annoyance inadvertently caused by the Steam sale that can't be stopped by Valve's special crowdsourced ban system.